1. Field of the Invention
The present invention relates to the purification of an alcohol from a fermentation broth.
2. Description of Related Art
The production of alcohol by microbial fermentation has many advantages. For example, the production of butanol, 1,3-propanediol and 1,2-propanediol by fermentation are well known. The raw material in the fermentation medium can be glycerol. The synthesis of 1,3-propanediol by fermentation of glycerol by clostridium has been described in particular. The synthesis of 1,3-propanediol by fermentation of glycerol provides a significant reduction in production costs compared to chemical synthesis using petroleum products.
The production of alcohols by fermentation is often accompanied by the production of organic acids and/or ketones. Thus, the production of 1,3-propanediol by microbial fermentation can be accompanied by the co-production of other products including acetone or acids in the form acetic and/or butyric acids or acetate and/or butyrate salt.
The alcohol produced by fermentation must then be purified from the fermentation broth. The fermentation broth can contain by-products that are also advantageous to purify (acetone, butyrate or acetate, for example) in addition to, typically, water, organic impurities, mineral salts and organic salts.
In the specific case of 1,3-propanediol, organic impurities responsible for 1,3-propanediol's color and odor are often observed. These impurities have not been identified but it is possible that they occur due to 1,3-propanediol degradation. Such degradation must thus be avoided during 1,3-propanediol production and purification.
A problem encountered during the purification of alcohol from fermentation broth is the elimination of salts. These salts are typically sodium chlorides and calcium chlorides but also ammonium and phosphate salts. The concentration of these salts in the fermentation broth controls their precipitation during alcohol purification.
Many methods for purifying 1,3-propanediol from fermentation broth have been described, notably EP 1,218.327, U.S. Pat. No. 7,056,439, EP 1,103,618 and WO2004/101479.
With regard to salts, most notably it has been proposed to eliminate salts upstream from the purification method by various techniques such as the use of ion-exchange resins (WO2004101479), electrodialysis (Gong et a)., 2006; Gong et al., 2004) and precipitation-filtration (U.S. Pat. No. 6,361,983).
However, these techniques do not always provide satisfactory results.
The present invention proposes a novel method for purifying an alcohol, notably 1,3-propanediol, from a fermentation broth.
Advantageously, the methods according to the present invention avoid the precipitation of salts during the purification of alcohol from the fermentation broth. In the inventive methods, the addition of glycerol solubilizes salts in order to retain them in the liquid phase until the end of the purification process.
Advantageously, the methods according to the present invention prevent the appearance of the impurities responsible for 1,3-propanediol color and odor.
According to another advantage of the present invention, the methods of the present invention provide improved yield.